Method and system for speech frame error concealment in speech decoding

1. A method for concealing errors in an encoded bit stream indicative of speech signals received in a speech decoder, wherein the encoded bit stream includes a plurality of speech frames arranged in speech sequences, and the speech frames include at least one partially corrupted frame preceded by one or more non-corrupted frames, wherein the partially corrupted frame includes a first long-term prediction lag value and a first long-term prediction gain value, and the non-corrupted frames include second long-term prediction lag values and second long-term prediction gain values, said method comprising the steps of:

providing an upper limit and a lower limit based on the second long-term prediction lag values;

determining whether the first long-term prediction lag value is within or outside the upper and lower limits;

replacing the first long-term prediction lag value in the partially corrupted frame with a third lag value, when the first long-term prediction lag value is outside the upper and lower limits; and

retaining the first long-term prediction lag value in the partially corrupted frame when the first long-term prediction lag value is within the upper and lower limits.

2. The method of claim 1 , further comprising the step of replacing the first long-term prediction gain value in the partially corrupted frame with a third gain value, when the first long-term lag value is outside the upper and lower limits.

3. The method of claim 1 , wherein the third lag value is calculated based the second long-term prediction lag values and an adaptively-limited random lag jitter bound by further limits determined based on the second long-term prediction lag values.

4. The method of claim 2 , wherein the third gain value is calculated based on of the second long-term prediction gain values and an adaptively-limited random gain jitter bound by limits determined based on the second long-term prediction gain values.

5. A speech signal transmitter and receiver system for encoding speech signals in an encoded bit stream and decoding the encoded bit stream into synthesized speech, wherein the encoded bit stream includes a plurality of speech frames arranged in speech sequences, and the speech frames include at least one partially corrupted frame preceded by one or more non-corrupted frames, wherein the partially corrupted frame includes a first long-term prediction lag value and a first long-term prediction gain value, and the non-corrupted frames include second long-term prediction lag values and second long-term prediction gain values, and a first signal is used to indicate the partially corrupted frame, said system comprising:

a first means, responsive to the first signal, for determining whether the first long term prediction lag is within an upper limit and a lower limit, and for providing a second signal indicative of said determining;

a second means, responsive to the second signal, for replacing the first long-term prediction lag value in the partially corrupted frame with a third lag value when the first long-term prediction lag value is outside the upper and lower limits; and retaining the first long-term prediction lag value in the partially corrupted frame when the first long-term prediction lag value is within the upper and lower limits.

6. The system of claim 5 , wherein the third lag value is determined based on the second long-term prediction lag values and an adaptively-limited random lag jitter.

7. The system of claim 5 , wherein the second means further replaces the first long-term prediction gain value in the partially corrupted frame with a third gain value when when the first long-term prediction lag value is outside the upper and lower limits.

8. The system of claim 7 , wherein the third gain value is determined based on the second long-term prediction gain values and an adaptively-limited random gain jitter.

9. A decoder for synthesizing speech from an encoded bit stream, wherein the encoded bit stream includes a plurality of speech frames arranged in speech sequences, and the speech frames include at least one partially corrupted frame preceded by one or more non-corrupted frames, wherein the partially corrupted frame includes a first long-term prediction lag value and a first long-term prediction gain value, and the non-corrupted frames include second long-term prediction lag values and second long-term prediction gain values, and a first signal is used to indicate the partially corrupted frame, said decoder comprising:

a first means, responsive to the first signal, for determining whether the first long-term prediction lag is within an upper limit and a lower limit, and for providing a second signal indicative of said determining;

a second means, responsive to the second signal, for replacing the first long-term prediction lag value in the partially corrupted frame with a third lag value when the first long-term prediction lag value is outside the upper and lower limits; and retaining the first long-term prediction lag value in the partially corrupted frame when the first long-term prediction lag value is within the upper and lower limits.

10. The decoder of claim 9 , wherein the third lag value is determined based on the second long-term prediction lag values and an adaptively-limited random lag jitter.

11. The decoder of claim 9 , wherein the second means further replaces the first long-term gain value in the partially corrupted frame with a third gain value when the first long-term prediction lag value is outside the upper and lower limits.

12. The decoder of claim 11 , wherein the third gain value is determined based on the second long-term prediction gain values and an adaptively-limited random gain jitter.

13. A mobile station, which is arranged to receive an encoded bit stream containing speech data indicative of speech signals, wherein the encoded bit stream includes a plurality of speech frames arranged in speech sequences, and the speech frames include at least one partially corrupted frame preceded by one or more non-corrupted frames, wherein the partially corrupted frame includes a first long-term prediction lag value and a first long-term prediction gain value, and the non-corrupted frames include second long-term prediction lag values and second long-term prediction gain values, and wherein a first signal is used to indicate the corrupted frame, said mobile station comprising:

a first means, responsive to the first signal, for determining whether the first long-term prediction lag is within an upper limit and a lower limit, and for providing a second signal indicative of said determining;

a second means, responsive to the second signal, for replacing the first long-term prediction lag value in the partially corrupted frame with a third lag value when the first long-term prediction lag value is outside the upper and lower limits; and retaining the first long-term prediction lag value in the partially corrupted frame when the first long-term prediction lag value is within the upper and lower limits.

14. The mobile station of claim 13 , wherein the third lag value is determined based on the second long-term prediction lag values and an adaptively-limited random lag jitter.

15. The mobile station of claim 13 , wherein the second means further replaces the first long-term gain value in the partially corrupted frame with a third gain value when the first long-term prediction lag value is outside the upper and lower limits.

16. The mobile station of claim 15 , wherein the third gain value is determined based on the second long-term prediction gain values and an adaptively-limited random gain jitter.

17. An element in a telecommunication network, which is arranged to receive an encoded bit stream containing speech data from a mobile station, wherein the speech data includes a plurality of speech frames arranged in speech sequences, and the speech frames include at least one partially corrupted frame preceded by one or more non-corrupted frames, wherein the partially corrupted frame includes a first long-term prediction lag value and a first long-term prediction gain value, and the non-corrupted frames include second long-term prediction lag values and second long-term prediction gain values, and wherein a first signal is used to indicate the corrupted frame, said element comprising:

a first means, responsive to the first signal, for determining whether the first long-term prediction lag is within an upper limit and a lower limit, and for providing a second signal indicative of said determining;

a second means, responsive to the second signal, for replacing the first long-term prediction lag value in the partially corrupted frame with a third lag value when the first long-term prediction lag value is outside the upper and lower limits; and retaining the first long-term prediction lag value in the partially corrupted frame when the first long-term prediction lag value is within the upper and lower limits.

18. The element of claim 17 , wherein the third long-term prediction lag value is determined based on the second long-term prediction lag values and an adaptively-limited random lag jitter.

19. The element of claim 17 , wherein the third means further replaces the first long-term prediction gain value with a third gain value when the first long-term lag value is outside the upper and lower limits.

20. The element of claim 19 , wherein the third gain value is determined based on the second long-term prediction gain values and an adaptively-limited random gain jitter.